Hydraulically driven equipment, such as lawn tractors, have had transaxle structure mounted in a casing including a drive input connection, a gear reduction drive, and oppositely-extending differentially-connected axle shafts. Typically, a hydrostatic transmission is connected to the exterior of the casing with a power output from the hydrostatic transmission driving the axle shafts to transmit power from the drive input to the transaxle.
Because of stringent packaging restrictions necessitated by the operating environments which are defined in the hydraulic equipment in which transaxles and hydrostatic transmissions are utilized, it is desirable to minimize the size of the assembled components without sacrificing performance capability of the transaxle.
One approach to providing a more compact transaxle has been to integrate the hydrostatic transmission with the transaxle components in a common casing. For example, as shown in prior U.S. Pat. No. 4,903,545 to Louis et al, dated Feb. 27, 1990, a transmission center section has been proposed for mounting the two hydraulic displacement units of a conventional hydrostatic transmission in perpendicular relation within a transaxle casing. While this construction has proven successful, the design has some limitations in very compact envelope or packaging applications.
As disclosed in the U.S. Pat. No. 4,903,545, an integrated transaxle utilizing the center section has a two-piece casing with the axle shafts, a hydraulic motor output shaft, and a counter-rotating intermediate shaft for transferring motion between the output shaft and the axle shafts, all of which are sandwiched between upper and lower casing parts. In order to align each of the shafts along the casing split line, it is necessary to arrange each of the components in a side-by-side, substantially parallel coplanar relationship. This type of arrangement requires an enlarged transaxle casing to envelope all of the juxtaposed shafts and associated components.
In addition, in the U.S. Pat. No. 4,903,545, in order to accommodate fluid passages for achieving communication between a hydraulic pump and the motor, the pump mounting surface is formed coplanar with the horizontal split line between the casing parts. The hydraulic pump is fixed to the pump mounting surface above the split line and has a vertically extending shaft which projects upwardly through the transaxle casing. Because the entire pump is positioned above the casing split line, the upper casing part must necessarily be sufficiently voluminous to house the pump, resulting in a large integrated transaxle package.
This invention is directed to further improvements in hydrostatic transaxles and which are specifically directed to reducing the packaging or envelope of the transaxle.